Digital imaging method and apparatus for detection of document security marks

ABSTRACT

A method and apparatus for preventing or inhibiting effective reproduction of documents such as currency, checks, stock certificates, and any other printed document including a pre-defined security mark printed therein. The subject method and apparatus operate to effect a multi-step review of all digital image data acquired from a printed document to be reproduced for purposes of locating any potential security marks and further examining same for purposes of positively identifying a potential security mark as an actual security mark. If a mark is located and verified to be an authentic security mark, effective reproduction of the printed document will not be permitted and/or other security measures will be taken.

BACKGROUND OF THE INVENTION

The present invention relates to the digital image processing arts. Moreparticularly, the application relates to a method and apparatus forpreventing or inhibiting effective reproduction of documents such ascurrency, checks, stock certificates, and any other printed documentincluding a pre-defined security mark printed therein. The subjectmethod and apparatus operate to effect a multi-step review of alldigital image data acquired from a printed document to be reproduced forpurposes of locating any potential security marks and further examiningsame for purposes of positively identifying a potential security mark asan actual security mark. If a mark is located and verified to be anauthentic security mark, effective reproduction of the printed documentwill not be permitted and/or other security measures will be taken.

The proliferation of digital image processing systems, such as digitalcolor copiers, that are able to make very high quality reproductions or“copies” of color documents at a low cost has led to use of thesemachines by criminals for reproduction of currency, checks, stockcertificates, legal documents, and other printed documents not legallyreproducible. Obviously, any reproductions of these documents arecounterfeit and illegal. Unfortunately, there has heretofore not beenfound a method or apparatus for effectively and efficiently detectingthe attempted reproduction of currency and the like so that thereproduction may be thwarted. Without an effective an efficientmethod/apparatus for detecting currency and other non-reproducibledocuments, criminals have often been able to produce counterfeitdocuments almost at will.

Many difficulties are presented during the attempted identification of asecurity mark in a printed document. The documents, such as currency,are often significantly worn. Also, the document may be placed in thereproduction apparatus at an irregular angle or location that rendersdetection of the security mark more difficult. Also, improper orerroneous detection of a security mark, and any resulting operations toprevent duplication of the document, are likely to upset andinconvenience those attempting to make legitimate reproductions.Accordingly, erroneous detection of a security mark in a document mustbe minimized.

Based upon the foregoing and other considerations, a need has been foundfor a new and improved digital imaging method and apparatus fordetection of document security marks to prevent production ofcounterfeit documents. It has been deemed desirable to develop such amethod and apparatus that perform this function in an effective andefficient manner, without intrusion into or interruption of legitimatedocument reproduction efforts.

SUMMARY OF THE INVENTION

In accordance with the present invention, a new and improved digitalimaging method and apparatus are provided for effective and efficientdetection of document security marks to prevent counterfeiting ofdocuments.

In accordance with a first aspect of the present invention, a method ofdigital image processing is provided. The method includes, for a printeddocument potentially including a security mark defined therein by aplurality of actual mark constituents each having a select color, size,and shape and having a select spatial arrangement relative to eachother, scanning the document to obtain digital image data correspondingto the printed document, the digital image data defined in terms of aplurality of color input pixel values. The digital image data isprocessed to identify all portions representing potential constituentsof a security mark. For each potential mark constituent represented bythe digital image data, it is determined if the potential markconstituent, together with at least one other potential mark constituentrepresented by the digital image data, defines a potential securitymark. For each potential security mark represented in the digital imagedata, it is determined if the potential security mark represents anactual security mark present in the printed document. In accordance withanother aspect of the present invention, a digital image processingmethod for preventing unauthorized reproduction of a printed documentincluding a security mark defined in terms of a plurality of actual markconstituents having a select color, select dimensions and arranged in aselect pattern relative to each other, includes scanning said printeddocument to derive color digital data representing the printed document,the color digital data defined in terms of a plurality of pixels eachhaving a color value. All pixels of the color digital data having acolor value representing a color at least approximating the select colorof the plurality of actual mark constituents are identified. A binarymap of the color digital data is constructed and defined in terms of“on” and “off” pixels, the “on” pixels corresponding to the identifiedpixels of the color digital data having color values at leastapproximating the select color of the plurality of actual markconstituents. The binary map is used to identify potential markconstituents defined by the “on” pixels and to identify at least oneneighborhood of plural potential mark constituents together defining apotential security mark. The potential security mark is identified as anactual security mark if the potential mark constituents thereof areuniform relative to each other. If an actual security mark isidentified, effective duplication of the printed document is prevented.

In accordance with still another aspect of the present invention, amethod of processing digital image data representing a color printeddocument that includes a security mark for purposes of identifying thesecurity mark represented in the digital image data includes processingthe digital image data to identify all portions thereof defining aselect color corresponding to the color of the security mark in theprinted document. For each portion of the digital image data definingthe select color, it is determined if the portion represents a potentialconstituent of a security mark in the printed document. The methodfurther includes, for each potential security mark constituentidentified in the digital image data, determining if the potentialsecurity mark constituent, together with at least one other potentialsecurity mark constituent, defines a potential security mark. Thepotential security mark constituents defining each potential securitymark are compared to each other to determine if they are uniform interms of color and size relative to each other. A potential securitymark is identified as a security mark represented in the digital imagedata if the potential security mark constituents of the potentialsecurity mark are sufficiently uniform in terms of the least color andsize relative to each other.

In accordance with another aspect of the present invention, a documentreproduction security method includes scanning a printed document toderive color digital image data representative of the printed document.The digital image data is processed to identify all pixels thereof in aselect color range used to define a security mark in the printeddocument. The digital image data is also processed to identify allconnected components comprising only pixels of the digital image data inthe select color range. The digital image data is processed to identify,as potential mark constituents, all of the connected components havingboth a size and shape corresponding to a predefined size and shape ofactual mark constituents defining the security mark in the printeddocument. The digital image data is further processed to establish aneighborhood of a select size about each potential mark constituent andto identify, as a potential security mark, all neighborhoods comprising:(i) a number of potential mark constituents greater than or equal to aminimum and less than or equal to a maximum number of actual markconstituents required to define a security mark; and (ii) potential markconstituents arranged relative to each other in a manner correspondingto the actual mark constituents defining the security mark in theprinted document. For each neighborhood identified as a potentialsecurity mark, the digital image data is further processed to identifythe potential security mark as an actual security mark if the potentialmark constituents in the neighborhood are uniform in terms of at leastsize and color. Effective reproduction of the printed document isprevented if the digital image data includes an actual security mark.

One advantage of the present invention is the provision of a digitalimaging document security mark detection method and apparatus thateffectively and efficiently detect document security marks uponattempted digital reproduction of a printed document including asecurity mark to prevent production of counterfeit documents.

A further advantage of the present invention resides in the provision ofa digital imaging method and apparatus that minimize false detection ofsecurity marks.

Still another advantage is found in the provision of a digital imagingmethod and apparatus that detect document security marks without regardto shift or rotation of the original document in the documentreproduction apparatus.

Still other benefits and advantages of the invention will becomeapparent to those of ordinary skill in the art upon reading andunderstanding the specification together with the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention may take form in various steps and arrangements of steps,and in various components and arrangements of components. The drawingsare only for purposes of illustrating preferred embodiments, and it isnot intended that they be construed to limit the invention in any way.

FIG. 1 is a block diagram illustrating an image processing system inaccordance with the present invention;

FIG. 2A illustrates a printed document such as a currency note,including a security mark;

FIGS. 2B and 2C show enlarged portions of the document illustrated inFIG. 2A for purposes of showing the features of the security mark;

FIG. 3 is a flow-chart illustrating an overall digital image processingmethod for detecting document security marks in accordance with thepresent invention;

FIG. 4 is a more detailed flow-chart illustrating a digital imageprocessing method of detecting document security marks in accordancewith the present invention;

FIG. 5A is a flow-chart illustrating the binarization step of a digitalimage processing method for detection of document security marks inaccordance with the present invention;

FIG. 5B illustrates the binary data resulting from application of thebinarization method of FIG. 5A to the digital image data obtained fromthe printed document of FIG. 2A;

FIG. 6A is a flow-chart illustrating the micro-detection step of adigital image processing method for detecting document security marks inaccordance with the present invention;

FIG. 6B diagrammatically illustrates a method of identifying connectedcomponents of binary image data in accordance with the presentinvention;

FIG. 6C diagrammatically illustrates evaluation of connected componentsize in accordance with the present invention;

FIG. 6D diagrammatically illustrates a connected component templatematching operation in accordance with the present invention;

FIG. 6E illustrates the portions of the binary image data of FIG. 5Bthat correspond to potential constituents of a security mark in theprinted document of FIG. 2A;

FIG. 7A is a flow-chart illustrating a macro-detection operation of adigital image processing method for detecting document security marks inaccordance with the present invention;

FIG. 7B illustrates the portions of the binary image data of FIG. 5Bthat correspond to potential security marks in the printed document ofFIG. 2A;

FIG. 8 illustrates a verification operation of a digital imaging methodfor detecting document security marks in accordance with the presentinvention; and,

FIG. 9 is a flow-chart illustrating control of the digital imageprocessing system to prevent effective duplication of a documentincluding a security mark.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring now to the drawings where the showings are for purposes ofdescribing preferred embodiments of the invention only and not forpurposes of limiting same, a digital image processing system 10 inaccordance with the present invention is shown in FIG. 1. An image inputscanner 12 derives and delivers digital image data in the form of one ormore monochromatic separations, wherein the picture elements or pixelsof each separation are defined at a depth of d bits per pixel where d isan integer. Accordingly, each pixel of each separation is defined interms of d bits per pixel (bit depth=d), and each pixel has some grayvalue between full off and full on. When the digital image data isprovided in terms of a single monochromatic separation, the image ismonochromatic, for example, so called black-and-white image data. On theother hand, when the digital image data is provided in terms of two ormore monochromatic separations, a color image results when the data fromthe separations is combined, for example, red-green-blue (RGB)separations or cyan-magenta-yellow (CMY) separations.

The image signals are input from the scanner 12 to an image processingunit 14 wherein digital image processing, such as security markidentification in accordance with the present invention, is performed.The image processing unit 14 may be provided by any suitable electroniccomputing apparatus such as an electronic computer, a dedicatedelectronic circuit, or any other suitable electronic circuit means. Theimage processing unit 14 outputs data in a suitable format to an imageoutput terminal 16 such as a digital printer and/or visual display.Suitable apparatus for digital image input and/or output include theXEROX Document Center 265DC digital imaging system, Pixelcraft 7650 ProImager Scanner, XEROX DocuTech Production Printing System scanners, theXEROX 5775 digital color copier, the XEROX 5760 and 5765 Majestikdigital color copiers, or any other suitable color digitalscanner/copier. Regardless of the depth d at which each pixel isdefined, the location of each pixel in each separation bitmap is alsodefined, typically in terms of a row “n” and a column “m.”

FIG. 2A illustrates a currency note including a security mark imprintedor otherwise included thereon. The illustrated currency note andsecurity mark are for ease of illustrating the invention only, and thoseof ordinary skill in the art will recognize that the invention isequally applicable to any type of document including any suitablesecurity mark thereon. As noted, checks, stock certificates, bonds, andlegal documents are some other examples of documents that may includesecurity marks and that may, consequently, be protected fromunauthorized reproduction according to the present invention.

The currency note 20 is printed on paper 22 or other suitable substrateand comprises various markings, such as denomination markings 24, text26, various decorative images and designs 28, and a security mark SMused to identify the currency note 20 as an authentic document. Asillustrated and described herein, the security mark SM is printed in thesame or similar manner on the document 20 as the information 24, 26, 28,typically using any suitable color ink.

With reference now to FIGS. 2B and 2C, the portion of the currency note20 including the security mark SM is illustrated and greatly enlarged toshow the characteristics of the security mark SM used in the presentexample. As noted, in practice, the security mark will likely take anyone of a wide variety of alternative forms, and the invention is not tobe limited to the illustrated or any other particular security mark. Inthe present example, the security mark SM is defined on the note 20(according to a definition promulgated by the appropriate authorities)by three identical mark constituents MC, each having identical size,shape and color according to the security mark definition. Also, themark constituents MC are arranged in a select pattern or arrangement asrequired by the definition of the security mark SM. As illustratedherein, the mark constituents MC are circular and arranged at thevertices of a right triangle. The mark constituents MC are separatedfrom each other by the distances D1, D2, D3, to define the security markSM further as having a select overall size and shape.

The apparatus and method in accordance with the present inventionoperate the image processing unit 14 to detect the existence of asecurity mark SM in a document such as the note 20 scanned by the imageinput scanner 12 so that the image processing unit can prevent orinhibit unauthorized reproduction of the note 20 or other document beingscanned. Those of ordinary skill in the art will also recognize that thesubject method hand apparatus may be used to determine the authenticityof a document.

With reference now to FIG. 3, a preferred digital image processingmethod for detection of document security marks is illustrated inaccordance with the present invention. The security mark detectionmethod as implemented using the digital imaging processing system 10comprises: S1—obtaining a digital input image, typically through use ofthe image input scanner 12; S2—binarization of the digital input image;S3 micro-detection; S4—macro-detection; S5—verification; andS6—prevention of the effective reproduction of the input document if asecurity mark is found. The operations S2 through S6 are preferablycarried out in the image processing unit 14.

The operations S1-S6 are illustrated in further detail in FIG. 4. Thestep S1 comprises scanning an input printed document, such as thecurrency note 20, using the input image scanner 12 to derive colordigital image data in terms of multiple color separations in a suitablecolor space, e.g., red R, green G, blue B, or the like. The scanner 12may derive or deliver the digital image data in terms of any othersuitable color space.

The binarization step S2 comprises a first sub-step S2 a of identifyingall pixels in the input digital image as derived by the scanner 12having or representing a color in a select range. A second sub-step S2 bconstructs a bitmap corresponding to all pixels of the input digitalimage identified as having a color in the select range.

The micro-detection operation S3 comprises sub-steps S3 a-S3 c. Moreparticularly, using the bitmap derived from the binarization operationS2, “connected components” in the bitmap are determined S3 a, and thoseof a size or shape not corresponding to a mark constituent MC arediscarded S3 b. Remaining connected components are identified aspotential mark constituents S3 c.

In the macro-detection operation S4, potential mark constituents inneighborhoods of other potential mark constituents that areover-populated or under-populated relative to a number of markconstituents MC defining a security mark SM are disregarded S4 a. Allremaining potential mark constituents that are not properly spaced fromor arranged relative to their neighbor potential mark constituents arealso disregarded S4 b, and only those still remaining are identified aspotential security marks S4 c.

Thereafter, all potential security marks are further analyzed foruniformity, e.g., uniformity of color, uniformity of size, and thosethat are not sufficiently uniform are discarded S5 a. Any remainingpotential security marks are positively identified as actual securitymarks SM. If an actual security mark SM is identified, the imageprocessing unit 14 prevents effective duplication of the documentscanned on the image input scanner 12, e.g., by completely terminatingthe digital image processing operation, by inserting a “VOID” message orthe like in the output data sent to the image output device 16, or byotherwise failing to output an exact replica of the input document, suchas the currency note 20.

The operations S1-S6 will now be described in further detail withreference to the currency note 20. In accordance with the operation S1,the currency note 20 is scanned to obtain digital image datarepresenting same in a suitable color space. This digital image data isfed to the image processing unit 14 for carrying out the operationsS2-S6 in accordance with the present invention.

With reference to FIGS. 5A and 5B, the binarization operation S2comprises constructing a bitmap 30 defined by a plurality of pixelscorresponding respectively in location to the plurality of pixelsdefining the input digital image of the currency note 20. To constructthe bitmap 30, the color of each pixel defined by the input digitalimage is examined by the sub-step S2 a to identify each pixel having acolor in a select range corresponding to the color used for the actualmark constituents MC in the security mark SM. For each pixel of inputimage data in the proper color range, a sub-step S2 b-1 sets thecorrespondingly located pixel in the bitmap to 1 or “on.” All otherpixels in the bitmap are set to 0 or “off” by the sub-step S2 b-2. Ofcourse, an initialization sub-step may alternatively be used to set allpixels in the bitmap 30 “off” prior to the color-checking sub-step S2 a.Using the binary digits “1” and “0” to represent “on” and “off”conditions corresponds with conventional computer science notation. Ofcourse, the binary digits “0” and “1” may alternatively represent “on”and “off,” respectively, and the invention is not intended to be limitedto either notation.

Those of ordinary skill in the art will also recognize that manydifferent methods exist for determining if a color of a pixel defined byvalues selected from a particular color space falls within a selectcolor range, i.e., whether the color defined for a pixel in a particularcolor space is “close enough” to a desired color. If the distance of theactual color from the desired color is greater than a color rangethreshold T, then the actual color is outside of the range and not“close enough” to the desired color. For example, if the pixels of theinput digital image representing the currency note 20 are each definedby the actual red, green, and blue values (R,G,B), and if a pixel of adesired color is defined by desired red, green, blue values (R′, G′,B′), then the distance of the color defined by the actual red, green,blue values R,G,B from the desired color defined by the red, green bluevalues (R′,G′,B′) may be calculated and compared to the threshold Taccording to:

T≧{square root over ((R−R′)²+(G−G′)²+(B−B′)²)}

Of course, those of ordinary skill in the art will recognize thatalternative methods exist for determining whether a color value of apixel of a digital image is within a select color range. The preferredmethod will vary depending upon the particular color space by which thepixel is defined. It is not intended that the present invention belimited to any particular color comparison method or any particularcolor space.

Referring now more particularly to FIG. 5B, the bitmap 30 resulting frombinarization S2 of the input digital image derived by the scanner 12 forthe currency note 20 is illustrated. For each pixel of the input digitalimage derived by the scanner that represents a color in a select colorrange encompassing the color used to print the security mark SM, thebitmap 30 is defined by a correspondingly located “on” pixel. One ormore of these “on” pixels are generally identified at 34 in FIG. 5B.Likewise, all other pixels defining the bitmap remain or are set to an“off” condition. These “off” pixels are collectively identified at 32 inFIG. 5B. Accordingly, the bitmap 30 includes or identifies only thosepixels from the input digital image that represent a color in the selectcolor range that approximates the actual color of the constituents MC ofthe security mark SM.

The bitmap 30 is further processed according to the micro-detectionoperation S3 as illustrated in FIGS. 6A-6D in accordance with thepresent invention. A first sub-step S3 a identifies all “connectedcomponents” in the bitmap 30. The operation of identifying connectedcomponents, by itself, from digital image data such as the bitmap 30 isa conventional operation and well known to those of ordinary skill inthe art of digital image processing, in particular, the art of opticalcharacter recognition (OCR). In the preferred embodiment illustratedherein, connected components in the bitmap 30 are identified asillustrated in FIG. 6B. Each “on” pixel 34 of the bitmap 30 is placed inthe center cell 38 of a 3×3 pixel matrix 36. All other “on” pixels 34encompassed in the matrix 36 are deemed to be part of the connectedcomponent CC including the pixel 34 in the central matrix cell orlocation 38. Therefore, each connected component CC of the bitmap 30comprises a single “on” pixel 34 or a group of “on” pixels 34, whereinthe pixels defining the group are each immediately adjacent to at leastone other pixel in the group.

Once each connected component CC in the bitmap 30 has been identified,each connected component CC is further examined by sub-steps S3 b-1,S3b-2 to determine if the connected component is a potential markconstituent. Referring also now to FIG. 6C, the sub-step S3 b-1 performsa size-checking operation on each connected component CC to determine ifeither its column width X or row height Y either (1) exceeds or (2)fails to meet the size of a mark constituent MC. If the connectedcomponent CC under consideration by the sub-step S3 b-1 is too large ortoo small in either dimension, it is bypassed. Preferably, the sizechecking sub-step S3 b-1 compares the width/height dimensions of eachconnected component CC to acceptable width/height size ranges ratherthan a select fixed value to account for printing, scanning, and othervariations.

Each connected component CC that satisfies the size requirements of thesub-step S3 b-1 must also survive a template-matching sub-step S3 b-2wherein the connected component CC is compared to and must match atleast one template of an actual mark constituent in order for theconnected component to be deemed a potential mark constituent b. Thistemplate-matching operation is diagrammatically illustrated in FIG. 6D.Both of the connected components CC1 and CC2 satisfy the size checkingsub-step S3 b-1. Thus, each is then compared to a template 40 includinga plurality of cells 42. Certain cells 42 of the template 40 are targetcells 44, arranged in the shape and size of a mark constituent MC. Inorder for a connected component CC1,CC2 to match a template, thetemplate is overlaid with the connected component, and at least a selectpercentage of the target cells 44 must match or correspond to the pixels34 defining the connect component CC1,CC2. Again, to account forprinting, scanning, and other variations, a perfect template match ispreferably not required. In FIG. 6D, the connected component CC1 matchesthe template 40, while the connected component CC2 does not.Accordingly, the sub-step S3 c identifies only the connected componentCC1 (and all other connected components that satisfy thetemplate-matching operation S3 b-2) as a potential mark constituent PMCas illustrated in FIG. 6E.

Referring now to FIGS. 7A and 7B, the bitmap 30 is further processedaccording to the macro-detection operation S4 in an effort to determinewhich, if any, of the potential mark constituents PMC, with otherpotential mark constituents, defines a potential security mark PSM. Asnoted with reference to FIG. 2C, an actual security mark SM is definedby actual marked constituents MC arranged in a specific pattern andspaced from each other by the distances D1,D2,D3.

Using this information, which is obtained from the definition of thesecurity mark SM, and for each potential mark constituent PMC, thesub-step S4 a-1 establishes a neighborhood about the potential markconstituent having a radius equal to or minimally larger than themaximum of the distances D1,D2,D3. A sub-step S4 a-2 determines thenumber of potential mark constituents PMC in the neighborhood, includingthe central or main potential mark constituent about which theneighborhood is established. The sub-step S4 a-2 compares the number ofpotential mark constituents in the neighborhood to the number requiredto define a security mark. If a neighborhood has too many or too fewpotential mark constituents compared to the number required to define asecurity mark, a sub-step S4 a-3 disregards or bypasses the potentialmark constituent about which the neighborhood is based, and anotherpotential mark constituent PMC is examined beginning at the sub-step S4a-1.

On the other hand, if the neighborhood established about a potentialmark constituent PMC comprises the number of potential mark constituentsrequired to define a security mark SM, the neighborhood is furtherexamined by the sub-step S4 b-1. Preferably, to account for the presenceof “noise” potential mark constituents PMC, a neighborhood with one ortwo extra potential mark constituents relative to the number required todefine a security mark SM is deemed to satisfy the sub-step S4 a-2 so asto be further processed by the sub-step S4 b-1 rather than discarded.

For neighborhoods having an acceptable number of potential markconstituents PMC, the sub-step S4 b-1 determines the distances betweeneach potential mark constituent and its neighbors. The sub-step S4 b-1then compares these distances to the predefined distances D1,D2,D3 ofthe security mark SM. The distances between potential mark constituentsPMC in a neighborhood must equal or be a super-set of the distancesD1,D2,D3 plus or minus a margin of error to account for printing,scanning, or other variations. If not, the sub-step S4 a-3 disregards orbypasses the potential mark constituent PMC about which the neighborhoodis based, and the next potential mark constituent is examined beginningwith the sub-step S4 a-1.

However, if the distances between potential mark constituents PMC in aneighborhood equal or are a super-set of the distances D1,D2,D3, asub-step S4 b-2 discards any noise potential mark constituents PMC inthe neighborhood and determines the position of the remaining potentialmark constituents PMC in the neighborhood relative to each other andcompares same to the relative position of the mark constituents MCdefining an actual security mark SM. More particularly, the sub-step S4b-2 identifies and then discards noise potential mark constituents PMCfrom a neighborhood based upon the distances determined by the sub-stepS4 b-1. Any potential mark constituents PMC not relevant to the resultof obtaining the distances D1,D2,D3 is deemed to be noise and discarded.

The sub-step S4 b-2 determines the relative positions of the potentialmark constituents PMC in a neighborhood, and compares same to thesecurity mark SM using any other wide variety of methods. A preferredmethod, which operates independent of any rotation or other shift due toscanning variations at the image input scanner 12 is to use thedistances as determined by the sub-step S4 b-1. In such case, thepotential mark constituents PMC in the neighborhood are examined todetermine if the distances separating the potential mark constituentsare arranged in the same sequence as the distances D1,D2,D3 of asecurity mark SM. Such a method operates independently of the vertical,lateral, or rotational placement of the potential mark constituents PMCin the bitmap 30. By way of example, two neighborhoods 50,52 (FIG. 6E)of potential mark constituents PMC satisfy the distance requirements ofthe sub-step S4 b-1. However, when the sub-step S4 b-2 examines therelative positions of the potential mark constituents PMC of eachneighborhood 50,52, only the neighborhood 50 satisfies the requirementthat the potential mark constituents PMC be positioned relative to eachother as illustrated in FIG. 2C—with the distances D1,D2,D3 encounteredsequentially when the potential mark constituents PMC are examined in aclockwise order. In an alternative embodiment, each potential securitymark PSM is matched against a series of security mark templates, whereinthe templates are devised so that, if the potential security markrepresents an actual security mark, one template will be matchedregardless of any rotational shift of the constituents of the potentialsecurity mark—i.e., the entire potential security mark will be comparedto a template of an actual security mark, wherein the templatesencompass every possible rotational arrangement in which theconstituents of the potential security mark could define an actualsecurity mark.

If a neighborhood does not satisfy the sub-step S4 b-2, the sub-step S4a-3 bypasses the potential mark constituent PMC about which theneighborhood is established and another potential mark constituent PMCis processed beginning with the sub-step S4 a-1. On the other hand, if aneighborhood satisfies the sub-step S4 b-2, the sub-step S4 c identifiesthe neighborhood as a potential security mark PSM (FIG. 7B), andprocessing in accordance with the macro-detection operation S4 continuesat S4 a-1 for the next potential mark constituent PMC not already partof a potential security mark PSM.

If the macro-detection operation S4 results in the identification of anypotential security marks PSM, processing continues with a verificationoperation S5 in accordance with the present invention as illustrated inFIG. 8. Because the binarization S2, micro-detection S3, andmacro-detection S4 operations all preferably rely upon “ranges” orotherwise allow some variation in connection with the identification ofpotential mark constituents and potential security marks in terms ofcolor, size, shape, and the like, it is possible that one or more of thepotential mark constituents PMC defining a potential security mark PSMare not actual mark constituents MC. Of course, in such case, thepotential security mark PSM would not be an actual security mark SM.Thus, to ensure that a potential security mark PSM is an actual securitymark SM, the potential security mark is subjected to a verificationoperation S5 in accordance with the present invention. Moreparticularly, for each potential security mark PSM, a verificationsub-step S5 a-1 examines the color of each potential mark constituentPMC defining the potential security mark PSM, and determines if thecolor of each potential mark constituent is sufficiently close to oruniform with the color of the other potential mark constituents PMCdefining the potential security mark PSM. It is preferred that thepotential mark constituents have a color that is equal or close to eachother. For example, if two potential mark constituents PMC haverespective colors that fall within the color range used in thebinarization color-checking sub-step S2 a, but the respective colorsthereof are found at extreme opposite ends of the acceptable colorrange, such potential mark constituents will not be deemed to exhibitsufficient color uniformity relative to each other to be actual markconstituents MC. Any potential security marks PSM not satisfying thecolor uniformity verification sub-step S5 a-1 are discarded by thesub-step S5 c.

For potential security marks PSM satisfying the color uniformityverification sub-step S5 a-1, a dimensional uniformity verificationsub-step S5 a-2 examines the potential mark constituents PMC fordimensional uniformity relative to each other. The dimensionaluniformity verification sub-step S5 a-2 examines the column width and/orrow height of each potential mark constituent PMC defining the potentialsecurity mark PSM for purposes of ensuring that the dimensions of thepotential mark constituents are consistent relative to each other.Again, for example, if one potential mark constituent PMC exhibitsdimensional characteristics relative to other potential markconstituents that vary by +/−5%, the potential mark constituent willfail the dimensional uniformity verification sub-step S5 a-2, and thesub-step S5 c will discard the relevant potential security mark PSM. Ifthe potential mark constituents PMC defining a potential security markPSM satisfy the verification operation S5, a sub-step S5B identifies thepotential security mark PSM as an actual security mark SM.

Subsequent to the verification operation S5, a prevention operation S6operates to prevent effective reproduction of the document scanned bythe image input scanner 12. A sub-step S6 a determines if an actualsecurity mark SM has been identified as present in the document beingscanned by the input scanner 12. If no security mark SM has been found,reproduction of the document is permitted. If, on the other hand, asecurity mark SM is identified, a prevention sub-step S6 b preventseffective duplication of the document scanned by the input scanner 12.This is accomplished using one or more suitable prevention operationssuch as disabling the image output device 16, not sending output datafrom the image processing unit 14 to the image output device 16,embedding or otherwise including a message (such as VOID) in the imagedata sent to the image output device 16 so that the message is visiblein the document reproduction, or by any other suitable method thatprevents an effective reproduction of the document scanned by the inputscanner 12.

The invention has been described with reference to preferredembodiments. Modifications and alterations will occur to others uponreading and understanding the preceding specification. It is intendedthat the invention be construed as including all such modifications andalterations insofar as they fall within the scope of the appended claimsor equivalents thereof.

Having thus described the preferred embodiments, what is claimed is: 1.A digital image processing method for preventing unauthorizedreproduction of a printed document including a security mark defined interms of a plurality of actual mark constituents having a select color,select dimensions and arranged in a select pattern relative to eachother, said method comprising: a. scanning said printed document toderive color digital data representing said printed document, said colordigital data defined in terms of a plurality of pixels each having acolor value; b. identifying all pixels of said color digital data havinga color value representing a color at least approximating said selectcolor of said plurality of actual mark constituents; c. constructing abinary map of said color digital data defined in terms of “on” and “off”pixels, said “on” pixels corresponding to said identified pixels of saidcolor digital data having color values at least approximating saidselect color of said plurality of actual mark constituents; d. usingsaid binary map, identifying potential mark constituents defined by said“on” pixels, said step of identifying potential mark constituents bysaid “on” pixels comprising: processing said pixels of said binary mapto identify groups of at least one adjacent “on” pixel and identifyingeach of said groups as a connected component; comparing dimensions ofeach connected component to the predefined select dimensions of anactual mark constituent comprising the steps of: comparing a width ofthe connected component to minimum and maximum width values of an actualmark constituent; comparing a height of the connected component tominimum and maximum height values of an actual mark constituent; onlyfor each connected component having both a width encompassed by saidminimum and maximum width values and having a height encompassed by saidminimum and maximum height values, comparing the connected component toat least one template, said connected component identified as apotential mark constituent if said connected component matches said atleast one template; e. using said binary map, identifying at least oneneighborhood of plural potential mark constituents together defining apotential security mark; f. identifying said potential security mark asan actual security mark if said potential mark constituents thereof areuniform relative to each other; and g. preventing effective duplicationof said printed document if an actual security mark is identified. 2.The digital image processing method as set forth in claim 1 wherein saidstep (f) of identifying an actual security mark comprises: comparing allpotential mark constituents of a potential security mark to each otherand identifying a potential security mark as an actual security mark ifthe potential mark constituents defining the potential security mark areuniform relative to each other in terms of at least color and size.
 3. Adigital image processing method for preventing unauthorized reproductionof a printed document including a security mark defined in terms of aplurality of actual mark constituents having a select color, selectdimensions and arranged in a select pattern relative to each other, saidmethod comprising: a. scanning said printed document to derive colordigital data representing said printed document, said color digital datadefined in terms of a plurality of pixels each having a color value; b.identifying all pixels of said color digital data having a color valuerepresenting a color at least approximating said select color of saidplurality of actual mark constituents; c. constructing a binary map ofsaid color digital data defined in terms of “on” and “off” pixels, said“on” pixels corresponding to said identified pixels of said colordigital data having color values at least approximating said selectcolor of said plurality of actual mark constituents; d. using saidbinary map, identifying potential mark constituents defined by said “on”pixels; e. using said binary map, identifying at least one neighborhoodof plural potential mark constituents together defining a potentialsecurity mark, said step of identifying at least one neighborhoodcomprising: establishing a neighborhood about the potential markconstituent; counting the number of potential mark constituents locatedin the neighborhood; comparing the number of potential mark constituentsin the neighborhood to the number of potential mark constituents used todefine an actual security mark; and identifying a neighborhood as apotential security mark only if the number of potential markconstituents therein is equal to or greater than the number of actualmark constituents required to define an actual security mark; f.identifying said potential security mark as an actual security mark ifsaid potential mark constituents thereof are uniform relative to eachother; and g. preventing effective duplication of said printed documentif an actual security mark is identified.
 4. The digital imageprocessing method as set forth in claim 3 wherein said neighborhoodestablished about each potential mark constituent has a radius basedupon a predefined maximum distance between any two actual markconstituents defining an actual security mark in said printed document.5. The digital image processing method as set forth in claim 3 furthercomprising, prior to identifying a neighborhood as a potential securitymark: determining the distances between potential mark constituents insaid neighborhood; and identifying a neighborhood as a potentialsecurity mark only if the distances between potential mark constituentsdefine a super-set of distances between actual mark constituents of anactual security mark in said printed document.
 6. A documentreproduction security method comprising: scanning a printed document toderive color digital image data representative of said printed document;processing said digital image data to identify all pixels thereof in aselect color range used to define a security mark in said printeddocument; processing said digital image data to identify all connectedcomponents comprising only pixels of said digital image data in saidselect color range; processing said digital image data to identify aspotential mark constituents all of said connected components having botha size and shape corresponding to a predefined size and shape of actualmark constituents defining said security mark in said printed document;processing said digital image data to establish a neighborhood of aselect size about each potential mark constituent and determining if anumber of potential mark constituents in the neighborhood is greaterthan or equal to a minimum and less than or equal to a maximum number ofactual mark constituents; only for neighborhoods having greater than orequal to a minimum and less than or equal to a maximum number ofpotential mark constituents required to define a security mark,identifying the neighborhood as a potential security mark if thepotential mark constituents in the neighborhood are arranged relative toeach other in a manner corresponding to the actual mark constituentsdefining said security mark in said printed document; for eachneighborhood identified as a potential security mark, processing saiddigital image data to identify said potential security mark as an actualsecurity mark if said potential mark constituents in said neighborhoodare uniform in terms of at least size and color; and preventingeffective reproduction of said printed document if said digital imagedata comprises an actual security mark.